DESCRIPTION: The overall aim is to examine the mechanisms underlying pathophysiologic changes in neural coding in the auditory nerves of animals aged in quiet. Over the past 10 years they have successfully developed the Mongolian gerbil as a model of human presbyacusis. In this proposal we focus on one cochlear potential in the gerbil model known to be affected by age: the endocochlear potential (EP) produced by the lateral wall system. We examine the relationship between the EP and neural coding in young and aged animals. Specific focus is on the effects of EP on the processing of temporal information in auditory nerve fibers, an aspect not yet addressed in the literature in the normal cochlea, much less in the presbyacusic cochlea. There are three specific aims. Specific aim 1 examines neural coding of timing information in the auditory nerves of young and quite-aged gerbils. Experiments include single fiber studies and population studies using the compound action potential (CAP). The hypothesis to be tested is that temporal coding in quiet-aged animals becomes deficient with age. Specific Aim 2 acutely manipulates the EP in old and young gerbils to test the hypothesis that the EP plays a fundamental role in the coding of temporal information in auditory-nerve activity. Specific Aim 3 examines neural coding under conditions of a chronically low EP in young gerbils. The lowered EP will be maintained by infusing furosemide into the cochlea with an implanted cannula and osmotic pump over periods ranging from weeks to months. Previous work supports the hypothesis that ;the quiet-aged gerbil cochlea can be modeled as an intact hair cell system operating under conditions of a low EP. The last aim will establish a model of presbyacusic cochlea in a young animal, thereby greatly enhancing the efficiency of studies of presbyacusis in animal models.